One of the most common methods of packaging data for transmission in a digital cellular communication system uses what is known as a “single-user” packet. With a single-user packet, a data set intended for a single user is encoded as a single packet and then transmitted to the intended user using an available transmission resource (i.e., traffic channel). A second type of packet that has seen increased use in recent years is the packet type known as a “multi-user” packet. Multi-user packets are formed by concatenating multiple data sets, each typically intended for a different user, into a single larger data set of multi-user data which is then encoded into a single packet. An example, of transmissions using single and multi-user packets is Voice over Internet Protocol (VoIP).
Typically, the size of the multi-user data set before encoding is equal to the sum of the sizes of the individual data sets, plus the addition of control information to identify which users have information within the multi-user packet, along with how much information that they have and where it is located within the concatenated set. The use of multi-user packets developed as a result of the advantages that they offer when small sets of data need to be transmitted. First, they allow very small packets to be concatenated and efficiently transmitted in a transmission resource which was designed for larger packet sizes. Second, they allow for a single set of error detection bits and encoder tail bits to be used for a group of data sets rather than requiring multiple sets of these overhead bits. Finally, the larger packet sizes which are obtained from the concatenation process enable better effective coding gains to be realized.
Often, the transmission process will employ a technique known as hybrid automatic repeat request (HARQ) in order to improve the performance of the transmission. In a HARQ transmission, the access network (AN), or equivalently base station, transmits an initial transmission to a wireless receiver. Then, it waits for an acknowledgment (ACK) or negative acknowledgment (NAK) indication from the wireless receiver. If the AN receives a NAK, then it repeats the transmission to the wireless receiver or sends additional parity information to the wireless receiver as the second transmission. This process is repeated until either the wireless receiver sends a positive acknowledgment or a pre-determined maximum number of transmissions is attempted without success. Typically, in order to make full use of the transmission capability of the channel, the transmitter may engage in the concurrent transmission of multiple sets of data. For instance, rather than waiting idle while the receiver determines acknowledgement based on the most recent transmission and signals this acknowledgement indication to the transmitter, the transmitter may initiate transmission of a second data set to the same or a different receiver. During the time required for the receiver to determine acknowledgment and signal this acknowledgement to the transmitter, the transmitter may also initiate the transmission of additional data sets to these same or different receivers in order to ensure that the transmitter is never waiting idle for acknowledgements. An example of this is the synchronous hybrid automatic repeat request (S-HARQ) technique employed in the current high rate packet data (HRPD) standard, which establishes a set of four time-division interlaced transmission channels which can be used for the concurrent transmission of four different sets of data. These interlaced transmission channels are sometimes referred to as “HARQ interlaces”.
Although HARQ enables improved performance of the radio link, it also introduces a certain amount of uncertainty as to when a positive acknowledgement might be obtained for a particular data set, which can itself introduce its own problems, especially when the data to be delivered is sensitive to delay, i.e. latency issues.
For example, consider a system consisting of N transmission resources that are being used to deliver voice or other delay-sensitive data to U users using the HARQ technique. Data sets arrive for all or some portion of the users on a somewhat periodic basis (e.g., every twenty milliseconds) and each user's data must be conveyed to it before a certain amount of time has passed (e.g., before the next twenty milliseconds has elapsed). In a heavily-loaded system with more users than transmission resources (i.e., U>N), the data sets corresponding to a subset of these users will be selected as the initial group of data sets to begin transmission. The remaining data sets will have to wait until transmission resources become available due to successful acknowledgement by one or more receivers. Once a transmission resource does become available, a latter-initiated data set is at a disadvantage due to its late start against the twenty millisecond maximum delay criterion and the associated limited number of HARQ transmission attempts that are available to it before the delay criterion expires. This ultimately leads to lower capacity in this type of system, since in order to maintain a given quality of service guarantee, the number of users beginning delayed packet starts must be limited.
Thus, there is a need for a method and system for effectively using transmission resources in a manner that mitigates the detrimental effects of late resource assignment and transmission starts in a communication system employing HARQ.
Skilled artisans will appreciate that many common but well-understood elements that are useful or necessary in a commercially feasible embodiment are not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.